The present invention relates to an amplifier arrangement.
Such an amplifier arrangement is already known in the art, e.g. from the U.S. Pat. No. 3,772,606 "Multi-level power amplifier". Therein, amplifier arrangements consisting of a series connection of 4 transistors are shown. Indeed, in FIGS. 2 and 3 of this prior art document, a first pair of transistors 39 and 40, constituting a first emitter follower is coupled via a pair of diodes between a first pair of power supplies delivering a first pair of bias voltages. A second pair of power supplies, delivering to a second pair of power supply terminals a second pair of bias voltages of the same polarity and of larger amplitude than the first pair, is coupled between the outermost transistors 44 and 49 of FIGS. 2 and 3 of this prior art document.
This configuration of 4 transistors in series, is generally known as the bipolar or push-pull variant of a class-G amplifier.
The four input terminals of this prior art class-G amplifier variant are coupled to the input signal source via bias means, the latter corresponding to the drive control circuit of claim 1.
In FIG. 2 of this prior art document, this bias means correspond to a pair of resistors, denoted 47 and 48. In FIG. 3, the transistors are coupled in a different way to the input signal source, by means of a series connection of the resistors 60,56,58 and 62, and the two diodes 64 and 66 . All these variants can however be considered as different embodiments of such a drive control circuit, which couples the input terminal of the arrangement to the different input terminals of the class-G power amplifier.
Such class-G power amplifiers have proven to be efficient from the point of view of power consumption. However, one major drawback is that they require a lot of silicon area if they have to be realized as an integrated circuit. Indeed, in for instance the bipolar or push-pull variant of the prior art embodiment, all four transistors have to be dimensioned such as to be able to deliver, resp. to sink, the largest possible power or current to, resp. from, the load. In applications such as audio amplifiers or Asymmetric Digital Subscriber Line amplifiers, this largest current is however only to be delivered in very exceptional circumstances. This is because the input signal has a high crest factor, meaning that in general, the input signal has a rather low average value, and that only in these very rarely occurring circumstances, the input signal peaks at this maximum level. Only in these circumstances this maximum current is to be delivered to the load. Nevertheless, since this high current is not only flowing through the transistors connected to the highest voltage power supplies, but also through the innermost transistors coupled to the lower voltage power supply, all four transistors are to be dimensioned to be able to carry these rarely occurring high currents.